https://gcc.gnu.org/g:a882b00403b809d2d69c87bb471afe17beb0c3e4
commit r15-11251-ga882b00403b809d2d69c87bb471afe17beb0c3e4 Author: Martin Uecker <[email protected]> Date: Sun May 10 20:21:40 2026 +0200 c23: fix TBAA error for function returning structure [PR125252] To fix PR122572 we globbed pointers to structure or union types nested within other structure or union types to a void pointer when computing the TYPE_CANONICAL. But when doing this for function return types this then leads to wrong aliasing decisions, because for some reason function derivation behaves differently than pointer and array derivation. Instead of globbing to void, replace the nested structure or union type with an incomplete type instead. PR c/125252 gcc/c/ChangeLog: * c-typeck.cc (ptr_to_tagged_member): Return type of member. (c_type_canonical): Use incomplete type. gcc/testsuite/ChangeLog: * gcc.dg/pr125252.c Diff: --- gcc/c/c-typeck.cc | 25 ++++++++++++++++--------- gcc/testsuite/gcc.dg/pr125252.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 52 insertions(+), 9 deletions(-) diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc index 96920a23a36e..f7464f899fef 100644 --- a/gcc/c/c-typeck.cc +++ b/gcc/c/c-typeck.cc @@ -561,8 +561,9 @@ c_reconstruct_complex_type (tree type, tree bottom) /* Helper function for c_canonical_type. Check whether FIELD contains a pointer to a structure or union with tag, - possibly nested in other type derivations. */ -static bool + possibly nested in other type derivations, and return the + type of this nested structure or union. */ +static tree ptr_to_tagged_member (tree field) { gcc_assert (FIELD_DECL == TREE_CODE (field)); @@ -580,17 +581,17 @@ ptr_to_tagged_member (tree field) if (ptr_seen && RECORD_OR_UNION_TYPE_P (type) && NULL_TREE != c_type_tag (type)) - return true; + return type; - return false; + return NULL_TREE; } /* For a record or union type, make necessary adaptations so that the type can be used as TYPE_CANONICAL. If the TYPE contains a pointer (possibly nested in other type - derivations) to a structure or union as a member, create a copy - and change such pointers to void pointers. Otherwise, the middle-end + derivations) to a structure or union as a member, create a copy and + change the nested type to an incomplete type. Otherwise, the middle-end gets confused when recording component aliases in the case where we have formed equivalency classes that include types for which these member pointers end up pointing to other structure or unions types @@ -617,9 +618,15 @@ c_type_canonical (tree type) for (tree x = TYPE_FIELDS (type); x; x = DECL_CHAIN (x)) { tree f = copy_node (x); - if (ptr_to_tagged_member (x)) - TREE_TYPE (f) = c_reconstruct_complex_type (TREE_TYPE (x), - ptr_type_node); + if (tree m = ptr_to_tagged_member (x)) + { + tree new_node = make_node (TREE_CODE (m)); + TYPE_NAME (new_node) = TYPE_NAME (m); + SET_TYPE_STRUCTURAL_EQUALITY (new_node); + new_node = qualify_type (new_node, m); + TREE_TYPE (f) = c_reconstruct_complex_type (TREE_TYPE (x), + new_node); + } *fields = f; fields = &DECL_CHAIN (f); } diff --git a/gcc/testsuite/gcc.dg/pr125252.c b/gcc/testsuite/gcc.dg/pr125252.c new file mode 100644 index 000000000000..4e27fa159782 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr125252.c @@ -0,0 +1,36 @@ +/* { dg-do run } */ +/* { dg-options "-std=gnu23 -O2" } */ + + +int k; +struct S {}; + +#define T struct S + +T *get_sender () { + k = 1; + return (void *)0; +} + +T *get_cc () { } + +void test () { + struct { + T *(*get_header) (void); + } reply_to_map[] = { + { get_sender }, + { get_cc }, + }; + + for (int i = 0; i < 2; i++) { + asm ("" ::"r"(reply_to_map[i].get_header ())); + } +} + +int main() { + test (); + + if (k != 1) + __builtin_abort(); +} +
